# Homework Help: Double slit problem (simple)

1. Dec 8, 2004

### vsage

single slit problem (simple)

A single slit diffracts laser light of wavelength 610 nm onto a screen 3.25 m away. The distance between the two first-order maxima on either side of the central peak is 3.65 mm. How wide is the slit (in mm)?

I figured the formula $$\lambda m = d sin(\theta)$$ would work but it's not. Here's my work:

sin(theta) = 3.65*0.5*10^-3 / 3.25 (since the angle is really small tan(x)~=sin(x))
sin(theta) ~= 5.62*10^-4

610*10^-9*1 = d * 5.62*10^-4

d~= 1.09mm or 1.09*10^-3m

This is wrong. What did I do wrong? Thanks

Last edited by a moderator: Dec 8, 2004
2. Dec 9, 2004

### Andrew Mason

Your formula uses the angle between the central peak and the first order MINIMA. That distance is 1/4 of 3.65mm.

AM